In vehicles in general, various different power train configurations occur, e.g. the gearbox may take the form of a manually operated gearbox or an automatic gearbox. In the case of heavy vehicles, it is often desirable for them to be drivable in as comfortable a way for the driver as possible, which usually entails the gear changes in the gearbox being effected automatically by means of the vehicle's control system. Gearboxes which change gear automatically have therefore also become increasingly usual in heavy vehicles.
This automatic gear changing is often effected in heavy vehicles by control system control of gear changes in “manual” gearboxes (also called AMT, automated manual transmission), partly because they are substantially less expensive to make, but also because of their greater efficiency.
The efficiency of automatic gearboxes of the type often provided in cars is far too low to be justified other than in, for example, urban buses and distribution vehicles which have frequently to come to a halt and then move off again.
“Manual” gearboxes which change gear automatically are therefore usual in heavy vehicles largely used on motorways/national highways.
This gear changing may be effected in various different ways, one of which involves using an automatically controlled clutch for up/downshifts, in which case the driver only needs access to an accelerator pedal and a brake pedal.
In principle, the clutch need only be used to set the vehicle in motion from stationary, as other gear changes can be effected by the vehicle's control system without using the clutch at all, since they are instead effected “torque-free”. It is also possible for the automatically controlled clutch to be used for only certain gear steps or only in upshifts or downshifts.
For comfort reasons, however, the automatically controlled clutch is in many cases used in all or substantially all upshifts and downshifts. On vehicles with automatic clutches, it is important to know the clutch's contact point (traction position), i.e. the position at which the clutch begins to transmit torque.
By knowing the contact point when for example the vehicle is moving off, coming to a halt and changing gear thus provides its control system with knowledge of the clutch position at which torque transfer from the engine to the rest of the power train begins or ends. This means that setting the vehicle in motion and changing gear can be effected in such a way as not to cause unacceptable jerking or unacceptable wear in the power train.
The contact point is however not a fixed position but may vary, e.g. because the clutch wears. It may also change when the vehicle is in motion, which means that even if it is determined at the beginning of a journey there is no certainty that the actual contact point later in the journey will correspond to that determined at the beginning.
There may thus be a need to effect contact point determination during a journey. Opportunities for doing so without disturbing the vehicle's driver may be more or less available depending on the environment on which the vehicle is travelling.
A problem with contact point determination is that the time it takes may be too long for it to take place unnoticed when the vehicle is in motion.
If the vehicle is for example travelling in urban traffic with many starts and stops, there may be good opportunities for doing contact point determination, e.g. when stationary at a red light. In the case, however, of vehicles mainly used on national highways, the number of possible opportunities may be significantly more limited. This is because the gearbox needs to be in neutral position for contact point adaptation to be possible. When the vehicle is travelling on national highways, there may be very long periods between any gear changes, particularly in low-lying areas. Contact point adaptation is therefore problematical in situations which involve no gear changes.
There is thus a need for an improved method for determining the contact point when the vehicle is in motion.